The experiments are directed towards understanding the role of calcium in the process of stimulus-secretion coupling. Emphasis is currently being placed on; (1) testing the sufficiency of the calcium ion to induce exocytosis and thus act as a true mediator, and (2) on defining the sources of calcium--cellular or extracellular--that are drawn on to effect the exocytotic response. BIBLIOGRAPHIC REFERENCES: Douglas, W.W. (1975). Secretomotor control of adrenal medullary secretion: synaptic, membrane, and ionic events in stimulus-secretion coupling. In: Handbook of Physiology. Section 7: Endocrinology. Vol. VI. Adrenal Gland (R.O. Greep and E. B. Astwood, Section eds.; H. Blaschko, G. Sayers and A.D. Smith, Vol. eds.). pp. 367-388. (Chapter 26). Washington D.C. American Physiological Society. Douglas, W.W. (1975). Stimulus-secretion coupling in mast cells: regulation of exocytosis by cellular and extracellular calcium. In: Calcium Transport in Contraction and Secretion, edited by E. Carafoli, F. Clementi, Wl Drabikowski, and A. Margreth. Amsterdam: North-Holland/American Elsevier.